Armed guards, a retinal scanner and a six-digit code on a keypad insure that only those "few" with special security clearance are allowed into the Office of Tailored Access Operations (TAO). The inner "sanctum" of TAO is "called the Remote Operations Center (ROC), which is where the unit's 600 or so military and civilian computer hackers (they themselves CNE operators) work in rotating shifts 24 hours a day, seven days a week." TAO "develops the information that would allow the United States to destroy or damage foreign computer and telecommunications systems with a cyberattack."
Foreign Policy's Matthew Aid wrote:
According to former NSA officials interviewed for this article, TAO's mission is simple. It collects intelligence information on foreign targets by surreptitiously hacking into their computers and telecommunications systems, cracking passwords, compromising the computer security systems protecting the targeted computer, stealing the data stored on computer hard drives, and then copying all the messages and data traffic passing within the targeted email and text-messaging systems. The technical term of art used by NSA to describe these operations is computer network exploitation (CNE).
The TAO's Remote Operations Center (ROC) is where US hackers break into targeted foreign systems by using special software developed by TAO's Data Network Technologies Branch to "download the contents of the computers' hard drives, and place software implants or other devices called 'buggies' inside the computers' operating systems," so TAO intercept operators can "continuously monitor the email and/or text-messaging traffic coming in and out of the computers or hand-held devices."
Yet another small group inside TAO, the Access Technologies Operations Branch, is responsible for "off-net operations," which Aid wrote, "is a polite way of saying that they arrange for CIA agents to surreptitiously plant eavesdropping devices on computers and/or telecommunications systems overseas so that TAO's hackers can remotely access them from Fort Meade."
China's "mountains of data" comment about the US hacking them is believed to mean specifically the TAO. As Aid pointed out, "As any high-stakes poker player knows, you can only press your luck so far when the guy on the other side of the table knows what cards you have in your hand."
Lots of people are upset about Snowden's NSA revelations, but The Foreign Policy article is greatly interesting and I cannot urge you strongly enough to go read it in full.
Sign up for CIO Asia eNewsletters.